1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a method and system for selecting control channels from base stations located near a border between radio telecommunications networks.
2. Description of Related Art
In a radio telecommunications network, when a mobile station (MS) originates a call, the MS scans for a control channel with the strongest signal. When an MS is operating along a border where two radio telecommunications networks having different network operators are adjacently located, the MS may access an analog control channel from a base station in a neighboring network rather than from the network in which the MS is operating. For example, an MS operating near a border within its home network may receive a stronger signal from a base station located across the border in a neighboring network and may access the neighboring network as a result.
Several problems arise when the MS accesses a control channel from a different operator. First, the MS is charged by a different network operator, rather than his home network operator. Second, higher rates, such as roaming charges, may result. Additionally, the home network operator loses revenue to which it is rightfully entitled since the MS is still operating within the coverage area of the MS's home network. The MS may also lose the ability to access features found in its home network.
Another serious problem arises when mobile stations operate along the border of two competing networks. In an attempt to recover lost revenue, network operators currently boost the transmitter power from their base stations in order to "capture" mobile stations operating along the border. Increasing the power of a base station in one network can lead to the bordering network operator boosting power from its base stations, literally causing a "power war" between the border base stations. The elevation of transmitter power at the border base stations leads to increased mutual radio interference along the border, decreasing the performance of both networks.
It would be advantageous to have a system and method which prevents mobile stations operating within their home network near a border with a neighboring network, from accessing analog control channels from the neighboring network. Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, a prior art reference that discusses subject matter that bears some relation to matters discussed herein is U.S. Pat. No. 4,905,301 to Krolopp et al. (Krolopp).
Krolopp discloses a mobile telephone which compares a system identification transmitted on a control channel of a desired network and the system identification transmitted on an access channel during the access process of the mobile telephone. Access is permitted only if the control channel system identification and the access channel system identification match.
Krolopp does not teach or suggest a system or method for correctly selecting control channels of base stations located near a border between radio telecommunications networks. Krolopp merely discloses a mobile telephone which compares a proposed control channel's system identification with a system identification obtained during initialization of the mobile telephone. Although Krolopp may be utilized to restrict a mobile telephone to operating on selected control channels, it suffers from several disadvantages. The mobile telephone must be modified to compare system identifications. Additionally, if the mobile telephone is turned on in a coverage area where an adjacent network's control channels have the strongest signal, the mobile telephone will access the adjacent network's control channel, since the preferred system identification is established when the mobile telephone is turned on. In fact, if the mobile telephone is turned on in the adjacent network, the mobile telephone will only allow access to control channels with a system identification associated with the adjacent network, even if the mobile telephone returns to the home network. Therefore, Krolopp only solves the problems of a mobile station transiting near a border when the mobile station is first powered on in its home network. Additionally, if the mobile telephone in Krolopp is actually located in the adjacent network, the mobile telephone will deny access for the strongest control channels, thereby losing revenue for the adjacent network operator which has a rightful claim on the lost revenue.
Thus, it would be a distinct advantage to have a system and method which prevents mobile stations operating within its home network along a border, from erroneously accessing analog control channels from another network with a different operator.